Noembed — oEmbed everything.

oEmbed is nice. Unfortunately, not everything supports oEmbed. Worse,
the sites that do support it don't provide a consistent
interface. Noembed provides a single url to get embeddable content
from a large list of sites, even sites without oEmbed support!

Additionally, Noembed guarantees that all responses will have
html, title, url, and
provider_name fields. This means fewer special
cases spent building up your own HTML.

Existing oEmbed Sites

Clyp

Flickr

Funny or Die

GIFUK

Hulu

Qik

Rdio

SlideShare

SoundCloud

Viddler

App.Net

Image Sites

CloudApp

Dropbox

Imgur

Imgur

Instagram

Lockerz

Path

Picplz

Skitch

Twitpic

Twitter

YFrog

The /providers endpoint

Noembed provides an endpoint that returns the
current list of supported sites. The response is a
JSON list with the site name and URL patterns. This can be used to automate testing if a URL is
supported by Noembed without making an HTTP request.

Similar sites

Oohembed was a very similar service. It even
acts as a gateway to non-oEmbed enabled sites like noembed. The main limitation that
I encountered was its lack of a guaranteed html field.

embed.ly. I have not tried this service, but it
lists support for hundreds of sites. Unfortunately, you can not add your own providers,
so you are limited to what they support. Oohembed users are now redirected to embed.ly.